The present invention relates, in general, to a transverse strut for a twist-beam axle of a motor vehicle.
It is generally known to use a torsion bar in addition to the transverse strut for a twist-beam axle for alignment of the track stiffness, camber stiffness and roll stiffness. Hereby, the functions, track stiffness, camber stiffness and roll stiffness, are substantially assumed by these separate components so that the afore-mentioned functions can be individually trimmed independently from one another. The use of a separate torsion bar is, however, disadvantageous and complicates the overall structure.
It would therefore be desirable and advantageous to provide an improved transverse strut for a twist-beam axle of a motor vehicle, which obviates prior art shortcomings and which is able to integrate in it the functions, track stiffness, camber stiffness and roll stiffness.
According to one aspect of the present invention, a transverse strut for a twist-beam axle of a motor vehicle is made of an extrusion profile and includes an outer tube and a bulbed land area extending inwardly from an inner wall surface of the outer tube and defined by a radial extension which is smaller than an inner radius of the outer tube, wherein the outer tube has a circumferential length and defines a central length portion which is positioned in confronting relationship to the bulbed land area and recessed to form a gap over a portion of the circumferential length.
The present invention resolves prior art problems by configuring the transverse strut through a combination of an outer tube as bending profile with an inner longitudinal bulbed land area which represents a torsion bar, so as to allow a trimming of the functions, track stiffness, camber stiffness and roll stiffness, independently from one another, without resorting to the use of separate components, as provided in the prior art. The bending strength of the transverse strut is hereby enhanced by the own inertia of the bulbed land area. In addition, as the bulbed land area is distanced from the common gravity center of the profile with the outer tube, the bending strength is positively influenced (Steiner""s theorem). Thus, the camber stiffness can be increased without the need for additional material. Also, the outer tube can be designed with better material use because the gravity of the transverse strut is shifted, as a result of the mass of the bulbed land areaxe2x80x94relating to the own gravity centerxe2x80x94in the direction of the bulbed land area. Material use is thus optimal at slight weight. Furthermore, the bulbed land area can be configured in an optimum manner to address tension concerns depending on the application at hand. It is also possible to change axial relationships to best suit various requirements as far as roll stiffness is concerned, by simply modifying the configuration and dimensions of the bulbed land area. Finally, the provision of a gap in longitudinal central length portion of the outer tube is able to impart the transverse strut with a reduced torsional stiffness.
According to another feature of the present invention, the outer tube defines a central cross plane and has opposite ends which are circumferentially closed, wherein the gap may extend approximately over half the circumferential length and has a circumferential length which gradually decreases to zero in the direction of the closed ends of the outer tube. In this way, the torsional stiffness can be further varied.
According to another feature of the present invention, the gap may have an axial length which is dimensioned in relation to an axial length of the closed ends at a ratio of about 4:1 to 6:1, preferably at a ratio of 5:1. Sizing the axial length of the closed ends of the outer tube depends on the requirements at hand, in particular on the type of connection between the transverse strut and longitudinal control arms of the twist-beam axle.
According to another feature of the present invention, the bulbed land area may have a tubular configuration. In this way, the roll stiffness can easily be modified. The bulbed land area may be formed interiorly with a closed longitudinal channel of a size, which can be dimensioned to best suit the application at hand.
According to another feature of the present invention, the bulbed land area has a radial wall extending inwardly from the inner wall surface of the outer tube to thereby distance the bulbed land area from the inner wall surface of the outer tube. In this way, the radial wall assumes the function of a thrust strut. Suitably, the radial wall extends in a longitudinal center plane of the outer tube and may have a radial height, which is greater than the inner radius of the outer tube.
According to another feature of the present invention, the radial height of the radial wall plus the radial extension of the bulbed land area can be dimensioned together in relation to an inner diameter of the outer tube at a ratio of about 0.8:1.4, preferably, about 1:1.2.
According to another feature of the present invention, the radial wall may have a thickness, which is approximately the same as a wall thickness of the outer tube. In this way, the thickness of the radial wall and the wall thickness of the outer tube can be suited to one another in an optimum manner so as to symmetrically distribute the edge fiber distance for the outer tube. Material consumption is reduced and weight is decreased. Suitably, the radial extension of the bulbed land area may be dimensioned at about three times the thickness of the radial wall.
Currently preferred is the production of the transverse strut from aluminum or aluminum alloy, although any material suitable for use in an extrusion process may be appropriate.